WO2015137797A1

WO2015137797A1 - Microstrip bandstop spurline filter

Info

Publication number: WO2015137797A1
Application number: PCT/MY2015/050013
Authority: WO
Inventors: Mandeep Singh JIT SINGH; Norbahiah MISRAN; Mohammad Tariqul ISLAM
Original assignee: Universiti Kebangsaan Malaysia
Priority date: 2014-03-12
Filing date: 2015-03-10
Publication date: 2015-09-17
Also published as: MY185701A

Abstract

The invention relates to a microstrip bandstop spurline filter (10). The present invention provides for adding spurline to microstrip filter to improve the performance of the filter. Under the present invention spurline is also implemented in microstrip filter to compare the performance between the different types of microstrip filter. Further under the present invention few designs for microstrip bandstop filters (BSF) are created and analyzed.

Description

MICROSTRIP BANDSTOP SPURLINE FILTER

Technical Field The present invention relates to the field of Electronics. More particularly, the present invention relates to the field of Microwave Circuit. Even more particularly, the present invention relates to a Microstrip filter used in microwave circuit. The present invention provides a Spurline Microstrip filter to improve the performance of the filter. Background of the Invention

The microstrip filter is widely used in microwave circuit nowadays. However, the good performance of microstrip filter requires large circuit size. Microstrip is a type of electrical transmission line which can be fabricated using printed circuit board technology, and is used to convey microwave-frequency signals. It consists of a conducting strip separated from a ground plane by a dielectric layer known as the substrate. Microwave components such as antennas, couplers, filters, power dividers etc. can be formed from microstrip, the entire device existing as the pattern of metallization on the substrate. Microstrip is thus much less expensive than traditional waveguide technology, as well as being far lighter and more compact. Most of the microstrip filters generally have lower power handling capacity, and higher losses.

A printed circuit board (PCB) mechanically supports and electrically connects electronic components using conductive tracks, pads and other features etched from copper sheets laminated onto a non-conductive substrate. Almost all the circuits encountered on electronics equipment are mounted on printed circuit boards. Conductors on different layers are connected with plated-through holes. PCBs are cheaper and faster to manufacture than other wiring methods as all the wiring is done with one component. Furthermore wiring errors are eliminated. PCBs contain a series of copper tracks printed on one or both sides of a fiber glass board or any other suitable insulator. The copper tracks form the wiring patterns required to link the circuit devices according to a given requirement. This removes the necessity of connecting insulated wires between components for any circuit. The resulting arrangement is cleaner and provides mechanical support for components. Further, the copper tracks are highly conductive and whole PCB can be easily reproduced for mass production.

There are a number of substrate types for PCB circuits. Substrate is essentially the base material of a PCB onto which the copper tracks and subsequent coating (e.g. Solder Resist) are applied. Examples of these materials are Fibreglass, SRBP, FR4, CEM1 , Polyimide, Duroid and Teflon. Specialist ceramic materials are often used for Hybrids. A commonly used material as a substrate for a PCB in high frequency designs is Duroid. There are a number of companies manufacturing PCBs which are based on Duroid. There are many problems found in the present technology in the field of microstrip filters.

Reference may be made to application number KR20120088234 (A), titled "Microwave Oscillator Using Symmetric Meander Spurline Resonator" by Bhanu Shrestha et al. dated 31 .01 .201 1 . This invention relates to a microwave oscillator using a symmetric meander spurline resonator is provided to improve band stop properties and band gap properties. CONSTITUTION: A microstrip line (120) is formed on a dielectric substrate (1 10). The thickness of the dielectric substrate is about 0.5mm to 0.6mm. A spurline is formed on the microstrip line. A meander slot (130) is formed from one end of the microstrip line in the vertical direction. The width (w) of the meander slot is about 0.1 mm to 0.2mm.

Reference may be made to application number CN 202121040 (U), titled "High Defect Coplanar Waveguide Double-Frequency Filter" by LINGQIN MENG dated 14.07.201 1 . This invention relates to a high defect coplanar waveguide double-frequency filter which is composed of a front side metallic signal layer, a middle layer, and a bottom layer, and is characterized in that the front side metallic signal layer has a section of central conduction band, the two sides of the central conduction band are grounding metal conductive planes, and the grounding conductive plane is provided with a spurline type defected ground structure and a short-circuited stub with the inductance coupling characteristic. The middle layer is a medium plate, the bottom of the medium plate is not provided with a metal coating. Compared with a conventional coplanar waveguide filter, the S1 1 in a pass band of the novel double-frequency filter is smaller, the in-band insertion loss is small, so the high defect coplanar waveguide double- frequency filter has an ultra-wide stop band characteristic, and restrains the first, the second, and the higher harmonic. The high defect coplanar waveguide double- frequency filter is simple in structure, high in processing precision, and is easy to operate and process. In addition, the filter only has one side, so the filter can be applied to the development of a multilayer board to realize the miniaturization.

Reference may be made to application number CN101950825 (A), titled "Novel Compact Dual-Mode Band-Pass Filter" by XUEHUI GUAN et al. dated 2006-05-10. This invention relates to novel compact dual-mode band-pass filter, which consists of a regular hexagonal fractal dual-mode resonator 3 of a dual spurline 4 loaded above the resonator and a pair of parallel coupling input/output port micro-strip feeder lines (1 , 6) for loading open circuit branches (2, 5), wherein the dual-mode micro-strip resonator consists of a compact hexagonal closed-loop resonator subjected to one-time Kohn fractal. The dual-mode effect is realized by the dual spurline loaded above the resonator; and the input and output ports of the filter have a non-orthogonal symmetrical structure. The novel compact dual-mode band-pass filter realizes circuit miniaturization by adopting a fractal structure on the premise of not increasing design difficulty, and the non-orthogonal symmetrical input/output port coupling structure solves the problem that the traditional input/output port is difficultly interconnected in a circuit during orthogonal arrangement. The novel compact dual-mode band-pass filter with the structure has the advantages of easy processing and manufacturing in actual use, and application to microwave integrated circuits. Reference may be made to United States Patent 8,384,498 titled "Capacitively loaded Spurline filter" by Grondahl et al. dated 26.02.2013. This invention relates to a spurline filter comprises a capacitive element connected to a spur and either a through-line of the Spurline filter or ground. In another embodiment, multiple capacitive elements are connected to the spur. In an exemplary embodiment, the capacitively loaded Spurline filter provides a band rejection frequency response similar to the band rejection frequency response of a similar Spurline filter that does not comprise at least one capacitive element but the capacitively loaded Spurline filter has half the layout area or less. In an exemplary embodiment, the Spurline filter comprises capacitive elements, where the capacitive elements are configured to reduce the resonant frequency of the filter.

Reference may be made to United States Patent 8,471 ,649 titled "Ku-band diplexer" by Devereux et al. dated 25.06.2013. This invention relates to a compact Ku band microwave diplexer configured as a three port surface mount component on a miniature alumina substrate. Input signals occurring at a common port having frequencies within a first pass band are passed to a second port while being isolated from signals occurring at a third port. Signals occurring at the third port are passed to the common port while being isolated from the signals at the second port. A microstrip dual spur line filter is used combined with open circuit stubs to provide enhanced second harmonic suppression on the transmit side, while using a coupled line microstrip filter on the receive side. This approach allows for compact size and automated component assembly through pick and place and reflow manufacturing techniques.

Reference may be made to United States Patent 6,414,639 titled "Resonance device, and oscillator, filter, duplexer and communication device incorporating same" by lio Kenichi dated 02.07.2002. This invention relates to a resonance device with strengthened coupling between a resonator and a transmission line without reducing an unloaded Q of the resonator. The resonance device includes a micro-strip line as a transmission line, which has a dielectric substrate, a main conductor, and an earth conductor, both of which are formed on the dielectric substrate, and a resonator disposed near the main conductor of the micro-strip line to be electromagnetically coupled thereto. At a part of the main conductor of the micro-strip line where it is coupled to the resonator, an electrode less portion such as a slit is formed in a direction substantially parallel to a signal-propagating direction.

There are a few non-patent literatures also present. Reference may be made to Bates et al. 1977, "Design of microstrip spur-line band-stop filters". In this case, the size of the device is bigger than present invention. Also this design is for 9 Ghz, whereas present invention is for 6 GHz.

So it is proved that there is no such device in the market with the features as of the device of present invention. The present invention increases the performance of the filter and overcomes the problems present in the already existing microstrip filters. The present invention aims to provide much better microstrip bandstop spurline filter than those in the prior art already. The present invention provides a unique microstrip bandstop spurline filter (1 0) . The present invention provides for adding the spurline to microstrip filter to improve the performance of the filter. Under the present invention the spurline is also implemented in microstrip filter to compare the performance between the different types of microstrip filter. Further under the present invention few designs for microstrip bandstop filters (BSF) are created and analyzed (Figure 1 ) .

Summary of the Invention The primary objective of the invention is to provide a microstrip filter.

Another objective of the invention is to provide a microstrip bandstop Spurline filter.

Another objective of the invention is to overcome the problem in prior art by reducing the original circuit size to obtain a better performance. Further objective of the invention is to create few designs of microstrip filters and analyze them for better performance of the circuit (Figure 1 ).

The present invention is a unique microstrip bandstop Spurline filter. The present invention provides for adding the spurline to microstrip filter to improve the performance of the filter. Under the present invention the spurline is also implemented in microstrip filter to compare the performance between the different types of microstrip filter. Further under the present invention few designs for microstrip bandstop filters (BSF) are created and analyzed (Figure 1 ). Under the present invention the circuit size can be made very small in comparison to the already existing circuits. The invention introduces the two open stubs that are suitable for wideband applications. The invention uses different types of PCB materials such as duroid.

Brief Description of the Drawings

Fig 1 shows various configurations of the microstrip filters:

(a) Spurline (10);

(b) Meander Spurline (15); and

(c) Without Spurline (20).

Fig 1 introduces the different type of microstrip filters with same circuit size, with or without the additional of spurline into it. The filter can obtain a better performance compared to the same size circuit without spurline. Fig 2 shows the schematic of measurement setup using E8362c PNA Network Analyzer. Further Fig 2 shows the

(a) Connection filters with equipment (25);

(b) Filter with a cable connection equipment (30) and

(c) Hardware of the design for microstrip bandstop spurline filter (35).

Fig 3 shows the simulation results insertion loss, S21 of the microstrip filter designs. Fig 4 shows the measurement and simulation results of S21 and S1 1 parameters for the BSF with spurline.

Detailed Description of the Invention

It should be noted that the particular description and embodiments set forth in the specification below are merely exemplary of the wide variety and arrangement of instructions which can be employed with the present invention. The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. All the features disclosed in this specification may be replaced by similar other or alternative features performing similar or same or equivalent purposes. Thus, unless expressly stated otherwise, they all are within the scope of present invention. Various modifications or substitutions are also possible without departing from the scope or spirit of the present invention. Therefore it is to be understood that this specification has been described by way of the most preferred embodiments and for the purposes of illustration and not limitation.

The present invention provides a novel and unique microstrip bandstop spurline filter (10), which is an improved version with much efficiency and quality in comparison to the already existing microstrip filters which are widely used in microwave circuit nowadays. Under this invention spurline is added to microstrip filter to improve the performance of the filter. Spurline is also implemented in microstrip filter to compare the performance between different types of microstrip filters. The filter under this invention has small circuit size 167.80 mm³ with wide stopband bandwidth 2.92 GHz with its stopband frequency 6.05 GHz at attenuation loss -60.2 dB and relative bandwidth by 48.3%. The filter is successful to miniature the circuit size by maximum 71 .6% and improves the bandstop bandwidth by 71 .8% and stopband frequency by 142.0% compared to other filters. The invention reduces the size successfully in order to save costs and to make the filter more compact and easily to attach with other equipment in the communication system. The microstrip bandstop filter at 3.01 GHz renders good quality of performance with small size of filter. The microstrip spurline filter (10) is having the capacity to reject harmonic and spurious responses in microwave and millimeter- wave circuits. The smaller size of the circuit area can be obtained with the embedment of spurline in the filter design. The microstrip spurline filter (10) has significant advantages over conventional bandstop filters when a moderate bandwidth bandstop filter is required. It is a very compact structure and also radiates power significantly less than conventional shunt stubs and coupled line filters. The microstrip filter under the present invention is also virtually dispersion-less and thus be used for terminating odd order harmonics of the stopband frequency. Basically there are two stubs i.e. Ag/4 apart and the stub length is also Ag/4 where Ag is the guided wavelength of the microstrip line at the center frequency. Normally more open stubs will be applied to obtain a deeper rejection and a wider stopband of an open stub filter but this would increase the design size and its insertion loss. Besides, spurline filter will only give the moderate rejection bandwidth. Thus the conventional open stubs and spurline will give another attenuation pole to achieve a deeper rejection and a better stopband without any incensement in circuit. However, meander spurline (15) filter will be seen to give a better stopband bandwidth than open stubs and Spurline filter design. The specific characteristic for FR4 used in the simulation substrate parameter such as substrate thickness 1 .58 mm, relative dielectric constant 4.4, copper conductor with 35 μιτι, and the loss tangent 0.022.

Comparison of the present invention with all other existing microstrip filters makes it easy to understand the efficacy and novelty of the present invention. A short comparison is made below to understand the present invention.

However, it should be understood that this comparative and analytical data is for the purposes of illustration only and therefore should not be construed to limit the scope of present invention. There are other alternative forms of the device which can be manufactured as per the requirement. The various alternatives are also within the scope of present invention only. Table 1 Comparison between microstrip bandstop filter with spurline and design of other journals

The size of proposed design microstrip bandstop filter with spurline (10) is 167.80 mm³ which is the smallest circuit size compared to other journals' designs. The reduction size is important in order to save cost and to make the filter more compact and easily to attach with other equipment in the communication system. The stopband frequency also increased compared to other designs which the proposed design achieved 6.05 GHz which is the highest among all the designs (Figure 3 and 4). The attenuation loss for the proposed design is considered quite high, which is -60.2 dB. The invention is designed for RFID and broadband applications. The wideband high-rejection microstrip band-stop filter is the highest for our design compared to the others. The proposed BSF shows a much deeper rejection and wider stopband than the conventional open- stub BSF without increasing the circuit size. By referring to the below mentioned table, one can understand the length of the invention. Table 2 Lengths of three proposed design filters in Millimeters

The simulation result of the present invention can be better understood by referring to the below mentioned table.

Table 3 Simulation results of three proposed microstrip filters by using IE3D software

From the Table 3 above, it can be shown that the among all the proposed design, the microstrip BSF with spurline (10) is having the best performance with its wider bandstop bandwidth (2.92GHz) and the higher stopband frequency (6.05GHz) at higher attenuation loss (-60.2dB). This design is also having improvement of its performance comparing to the other journal's designs. From the simulation result of three proposed filter designs shown in Figure 3, it is shown that the microstrip BSF with spurline (10) will have the best characteristic result among all the filter design performances. In these three proposed filter, all of them are having a small circuit size, 167.80 mm3. Embedment of spurline in microstrip BSF (10) is able to achieve the wider bandstop bandwidth 2.92GHz (5.29-8.21 GHz) with the small circuit size compared to other designs. Microstrip BSF without spurline (20) showed a poor performance since the stopband bandwidth cannot be considered since the attenuation loss did not less than the minimum requirement -20dB. However, BSF with meander spurline (15) will show better performance with bandstop bandwidth 2.23GHz (4.95-7.18GHz) than BSF without spurline (20) but less improvement performance if compared with design of BSF with spurline (10).

So accordingly, the present invention provides an improved microwave filter device with better performance, said filter comprising spurline embedded in the microstrip bandstop filter in the form of a microstrip bandstop spurline filter (10), so as to improve the performance of the microwave circuit filter, wherein said filter comprises plurality of open stubs that are suitable for wideband applications, said device uses different types of PCB materials and is miniature with circuit size resulting in reduction in size and improvement in bandstop bandwidth.

In an embodiment, said device comprises preferably two stubs (10).

In another embodiment, said two stubs are mainly Ag/4 apart, where Ag which is defined herein as the guided wavelength of the microstrip line at the center frequency.

In another embodiment, the stub length is also Ag/4, where Ag is defined herein as the guided wavelength of the microstrip line at the center frequency.

In another embodiment, said device may comprise more open stubs to obtain a deeper rejection and a wider stopband of an open stub filter as per the requirement at the cost of increase in device size and loss of insertion. In another embodiment, said device preferably comprises a small circuit size of 167.80 mm³ with wide stopband bandwidth 2.92 GHz.

In another embodiment, said device is very cost effective and is compatible with other equipment in the communication system.

In another embodiment, said device is miniature with circuit size preferably 167.80 mm³, which is the smallest circuit size with higher efficiency. In another embodiment, said device reduces the size by up to 71 .6% and improves the bandstop bandwidth by 71 .8% and stopband frequency by 142.0% as compared to other filters.

In another embodiment, said device renders good quality of performance with small size of filter at 3.01 GHz.

In another embodiment, said device is capable of functioning stopband frequency by 142.0%. In another embodiment, said device comprises stopband frequency of 6.05 GHz which is highest among all the already existing filters.

In another embodiment, said device comprises attenuation loss of -60.2 dB relative bandwidth by 48.3%.

In another embodiment, said device is having the capacity to reject harmonic and spurious responses in microwave and millimeter- wave circuits.

In another embodiment, said device is also compatible with plurality of open stubs.

In another embodiment, said device shows a much deeper rejection and wider stopband than the conventional open-stub BSF without increasing the circuit size. Advantages of the invention:

• Improved version with much efficiency and quality

• The filter under this invention has small circuit size 167.80 mm³

· The invention is successful to miniature the circuit size by maximum 71 .6%

• Improves the bandstop bandwidth by 71 .8%

• Improves stopband frequency by 142.0% compared to other filters

• Cost effective with compact in size

• Good quality of performance with small size of filter

· Very compact structure and also radiates power significantly less than conventional shunt stubs and coupled line filters.

Claims

1. An improved microwave filter device with better performance, said filter comprising;

Spurline embedded in the microstrip bandstop filter so as to improve the performance of the microwave circuit filter,

wherein said filter comprises plurality of open stubs that are suitable for wideband applications,

said device uses different types of Printed Circuit Board (PCB) materials and is miniature in circuit size resulting in reduction in size and improvement in bandstop bandwidth.

2. The device as claimed in claim 1 , wherein said device comprises preferably two stubs.

3. The device as claimed in claim 1 , wherein said Spurline is embedded in the microstrip bandstop filter in the form of a Microstrip Bandstop Spurline Filter.

4. The device as claimed in claim 1 , wherein said two stubs are mainly Ag/4 apart, where Ag which is defined herein as the guided wavelength of the microstrip line at the center frequency.

5. The device as claimed in claim 1 , wherein the stub length is also Ag/4, where Ag is defined herein as the guided wavelength of the microstrip line at the center frequency.

6. The device as claimed in claim 1 , wherein said device may comprise more open stubs to obtain a deeper rejection and a wider stopband of an open stub filter as per the requirement at the cost of increase in device size and loss of insertion.

7. The device as claimed in claim 1 , wherein said device preferably comprises a small circuit size of 167.80 mm³ with wide stopband bandwidth 2.92 GHz.

8. The device as claimed in claim 1 , wherein said device is very cost effective and is compatible with other equipment in the communication system.

9. The device as claimed in claim 1 , wherein said device is miniature with circuit size preferably 167.80 mm³, which is the smallest circuit size with higher efficiency.

10. The device as claimed in claim 1 , wherein said device reduces the size by up to 71 .6% and improves the bandstop bandwidth by 71 .8% and stopband frequency by 142.0% as compared to other filters.

11. The device as claimed in claim 1 , wherein said device renders good quality of performance with small size of filter at 3.01 GHz.

12. The device as claimed in claim 1 , wherein said device is capable of functioning stopband frequency by 142.0%.

13. The device as claimed in claim 1 , wherein said device comprises stopband frequency of 6.05 GHz which is highest among all the already existing filters.

14. The device as claimed in claim 1 , wherein said device comprises attenuation loss of -60.2 dB relative bandwidth by 48.3%.

15. The device as claimed in claim 1 , wherein said device is having the capacity to reject harmonic and spurious responses in microwave and millimeter- wave circuits.

16. The device as claimed in claim 1 , wherein said device is also compatible with plurality of open stubs.

17. The device as claimed in claim 1 , wherein said device shows a much deeper rejection and wider stopband than the conventional open-stub BSF without increasing the circuit size.